Navegando por Autor "Machado, Fernando Luis de Araujo"
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Item On the magnetic properties of the multiferroic ceramics Bi0:99Y0:01Fe1-xNixO3 Bi0:99Y0:01Fe1 xNixO3(2018) Ratkovski, Danilo Roberto; Ribeiro, P. R. T.; Machado, Fernando Luis de Araujo; Banerjee, Prasun; Franco Júnior, AdolfoMultiferroic ceramics of Bi0:99Y0:01Fe1 xNixO3 with 0:01 6 x 6 0:05 were synthesized by using a modified solid state reaction method. The crystalline structure and the morphology of the samples were investi gated by X-ray diffraction (XRD) and by scanning electron microscopy (SEM). The addition of Y and Ni to the bismuth ferrite (BiFeO3) was found to decrease the average grain size. Ac magnetic susceptibility and the zero-field-cooled (ZFC) and field-cooled (FC) magnetizations were measured for temperatures in the range 5 6 T 6 300 K. Hysteresis loops and an irreversible behavior in the temperature dependence of the magnetization not present in pure BiFeO3 were observed in the doped samples. However, the ferro magnetism was found more likely to be due to the presence of small amounts of magnetite. Nevertheless, the determination of the amount of Fe3O4 in these composite materials is important because it influences the magnetoelectric coupling which is important for some technological applicationsItem Specific heat measurements in pure and in (Cu, Mn, Fe, Ni)-doped single-crystals of l-arginine phosphate monohydrate(2010) Machado, Fernando Luis de Araujo; Sousa, Lázaro Luis de Lima; Cunha, R. O.; Cabral, F. A. O.; Rodrigues, Alexandre Ricalde; Carvalho, Jesiel Freitas; Santana, Ricardo Costa deThe influence of highly diluted impurities (Cu, Mn, Fe, Ni) on the temperature (T) dependence of the specific heat (cp) of l-arginine phosphate monohydrate (LAP) was investigated in the temperature range 1.8–300 K. The doped samples yielded values for cp in excess to those obtained for a pure LAP sample. The melting temperatures (Tm≈420 K) obtained by differential scanning calorimetry for pure and doped LAP samples were found not to be significantly affected by the impurities. The T-dependence of cp was fully accounted for by taking into consideration the Debye contribution, an Einstein term and a contribution due to both Frenkel and Schottky defects. The model fit all cp versus T data using a single value for both the Debye (θD=160 K) and the Einstein (TE=376.8 K) temperatures, and for the energy (εd=157.9 meV) required to create the defects.